Delphinus

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Delphinus or the Dolphin is a small constellation in the northern hemisphere. It was created by the Greek astronomer Ptolemy in the 2nd century. In Greek mythology, Delphinus is identified with the dolphin that helped the god Poseidon win over Amphitrite, a Nereid who had been fleeing from his advances. The dolphin was able to change her mind and, out of gratitude, Poseidon placed its image in the sky. In another tale, Delphinus is associated with the dolphin who saved the life of the Greek poet Arion of Lesbos. Arion was returning home with the fortune he had amassed on his travels and the crew of the ship started plotting to kill him and steal the fortune. Faced with death, his last wish was to sing a dirge. As he sang, he jumped into the sea and was saved by a dolphin which had been enchanted by his music. The Arabs called the constellation Al Ka'ud ("the Riding Camel"), while Indians also associate it with a dolphin.

The constellation Delphinus occupies an area of 189 square degrees and contains four stars with known planets. It lies near the celestial equator and can be seen at latitudes between +90° and -70°. It is best visible at 9 p.m. during the month of October.

The four main stars in the constellation – [3358] alpha, [3357] beta, [3365]-[3360] gamma and [3361] delta Delphini – form a prominent asterism known as Job’s Coffin. The two brightest stars, [3358] alpha and [3357] beta Delphini, were named Sualocin and Rotanev respectively in a star catalogue published at the Palermo Observatory in Italy in 1814. Backwards, they spell the name Nicolaus Venator, which is a Latinized version of the name Niccolò Cacciatore. (Venator and Cacciatore both mean "hunter.") Cacciatore was the assistant director of the observatory at the time. Both Sualocin and Rotanev are multiple stars; Sualocin with seven and Rotanev with five components.

[3365]-[3360] gamma Delphini, located at the tip of the dolphin’s nose, is a binary star. Its [3365] primary component is a yellow-white dwarf and the [3360] companion is an orange subgiant. They are approximately 101 light-years distant.

[3359] epsilon Delphini or Deneb Dulfim ("tail of the dolphin") is a blue-white giant about 358 light-years away from Earth.

[3361] delta Delphini is a double star with two identical members too close together to be discerned without a telescope. It is classified as a metal-rich class A giant, possibly a F0 subgiant, about 207 light-years distant.

[3363] rho Aquilae or Tso Ke is a white dwarf about 154 light-years distant. Before 1992, it was part of the constellation Aquila, but then moved across the border to Delphinus.

Delphinus contains several notable deep sky objects. NGC 6891 is a relatively small, bluish planetary nebula that can be seen close to [3363] rho Aquilae. NGC 6905 is another relatively small, blue planetary nebula. It is also known as the Blue Flash Nebula and can be seen in a 6-inch scope. NGC 6934 is a bright, large globular cluster that lies in a rich field of stars close to [3359] epsilon Delphini. NGC 7006 is a remote, relatively bright globular cluster, round in shape and located close to [3365]-[3360] gamma Delphini.